Maintenance of adequate pressure in pneumatic tires is acknowledged as a critical requirement. In particular, high performance tires used on the wheels of modern aircraft of large size and heavy weight, which land at high speeds have a critical requirement for accurate tire pressure.
In practice, in the maintenance of aircraft and other vehicles employing pneumatic tires such as highway trucks, and off the road vehicles, it is difficult and in some cases impossible to provide a regulated source of pressurizing gas to prevent over inflation. Also, high performance tires are often inflated with nitrogen in order to reduce the oxidation of such tires at high temperatures. Nitrogen is further preferred because of the relatively large size of its molecule, in comparison to the other constituents of air, which reduces tire leakage. A convenient and economic source of nitrogen is a high pressure tank wherein the delivered nitrogen is regulated from a typical tank pressure of 3,000 P.S.I.G., down to a tire delivery pressure, which typically is 300 P.S.I.G.
However, conventional tank regulators are often inaccurate in regulated output pressure, or fail to control delivery flow, or in many cases limit the delivery flow to low values that result in excessive inflation time. Also in many cases, it is exigent to utilize unregulated sources, such as secondary tanks filled to an intermediate pressure from a primary source. These secondary tanks are in common use and are economical, convenient and normally do not have an attached regulator. Tire filling or pressurization from an unregulated, secondary tank is essentially a cut and try operation. The usual technique involves approaching a desired pressure by gauging and filling in small steps. Since individual filling steps are by "feel", over pressurization can easily occur.
The avoidance of over pressurization is critical because it can cause excessive tire wear, loss of structural integrity and in extreme cases explosive failure. In many cases these explosions have caused serious injury and death to attending personnel. Unfortunately, the correct inflation pressure varies from vehicle to vehicle, and varies with location on a vehicle. Therefore, if a regulator is present on the pressure source, it constantly must be adjusted. Every time a regulator is adjusted, there is a chance that it will be improperly adjusted.
In view of the above mentioned difficulties, it is desireable to provide means to accurately regulate flow and delivery pressure for each individual tire. In this way correct inflation is assured.
These difficulties including safety related difficulties encountered with presently used tire pressurizing valves are overcome through the use of Applicants' invention. As disclosed, Applicants' invention provides a small, light weight and economical self-contained pressure and flow limiting valve as a replacement for the conventional tire valve. In use, the valve of the invention provides pressure relief and limits flow there through when in the relief position through positive shutoff, providing a convenient means for rapidly maintaining tire pressure from unregulated sources.
It is therefore an object of this invention to provide a pneumatic tire pressurization valve incorporating pressure relief at a predetermined pressure setting along with further overpressure protection through flow limiting and positive shutoff of the pressurizing gas when the valve is in its relief position.
It is an additional object of this invention to provide a pneumatic tire fill valve having size, weight, and cost features which allow permanent mounting on individual tires, thereby providing automatic control of tire pressurization without the need for a separate tire gauging operation.
It is a further object of this invention to provide a small, lightweight and economically designed tire fill valve directly replacing the individual original tire valve, wherein correct tire pressure can be assured even when the tire fill gas source is of substantially greater pressure and flow capacity than the tire and the valve respectively.
It is yet an additional object of this invention to reduce the danger to maintenance personnel, engaged in pressurizing a high pressure pneumatic tire from a source having excessive pressure and flow capacity, through the use of a pressure and flow limiting valve continuously attached to the tire.